Layered product

ABSTRACT

Sheet-like structures comprising rubber layers and fluoropolymer layers can be produced by employing, as adhesive layer, a mixture comprising a rubber and a thermoplastic fluoropolymer having a melting point &lt;250° C.

DESCRIPTION

Shaped articles and coverings made from natural and synthetic rubber arewidely used in industry. A disadvantage of these materials is theirrelatively low resistance to aggressive chemicals, in particular atelevated temperatures. There has, therefore, been no lack of attempts tocoat rubber with the much more highly resistant fluoropolymers. Theseattempts failed, however, because the conventional bonding andvulcanization processes do not permit a sufficiently strong bond to thefluoropolymer.

There has also been no lack of attempts to employ fluorinatedthermoplastics for this purpose, in particular copolymers oftetrafluoroethylene with such amounts of comonomers that the product isprocessable from the melt. However, even these copolymers, which intheir properties come close to elastomers, do not adhere to rubbers.

Surprisingly, it has now been found that excellent adhesion betweenrubbers and fluoropolymers can be produced when a formulation comprisinga rubber and from 10 to 70% by weight of a thermoplastic fluoropolymerhaving more than about 35% by weight of units of tetrafluoroethylene andalso units of hexafluoropropene and of vinylidene fluoride having amelting point <250° C. is employed as primer layer.

Further aspects and particular embodiments of the invention areexplained in greater detail in the claims.

The invention therefore relates to a composition essentially consistingof a rubber and of the thermoplastic fluoropolymer as described.

The terpolymers of tetrafluoroethylene, hexafluoropropene and vinylidenefluoride have thermoplastic properties if they contain more than about35% by weight of tetrafluoroethylene. Such terpolymers are known, forexample, from U.S. Pat. No. 4,335,238 and DE-A 26 35 402 (AU-A76/16635). Suitable terpolymers comprise from about 40 to about 60% byweight of tetrafluoroethylene, from about 10 to about 40% by weight ofhexafluoropropene and from about 10 to about 40% by weight of vinylidenefluoride.

EP-A-0 428 158 relates to a vulcanizable polymer composition made from acrosslinkable hydrocarbon elastomer, a polymer based on vinylidenefluoride and a crosslinking agent. After vulcanization, this can be usedto produce a packaging material of increased chemical and heatresistance. A copolymer made from vinylidene fluoride,tetrafluoroethylene and hexafluoropropene, inter alia, is included inthe vinylidene-fluoride-based copolymers mentioned.

U.S. Pat. No. 4,942,906 relates to a rubber hose with an outer and aninner rubber layer, the inner layer being composed in its turn of twolayers. The layer situated on the inside is formed from a first polymermixture made from acrylic rubber and from a fluorine-containing resin,and the outer layer is formed from a second polymer mixture whichdiffers from the first polymer mixture and comprises an epichlorohydrinrubber. The fluorine-containing resins listed are homopolymers andtetrafluoroethylene-hexafluoroethylene copolymers, and alsoethylene-tetrafluoroethylene copolymers, but no terpolymers.

U.S. Pat. No. 4,041,207 describes a heat-resistant rubber laminate whichessentially consists of a rubber layer made from a heat-resistant rubbermixture and a heat-resistant outer layer made essentially fromethylene-fluoropropylene elastomer.

The novel composition thus bonds on the one hand to rubber and on theother hand to (a layer of) the fluoropolymer as described. Thisfluoropolymer bonds in turn to layers of other fluoropolymers. In thisway, layered products of many varied types, comprising layers of rubberand of fluoropolymers and thus combining the properties of these twoclasses of materials, can be produced.

The fluoropolymers can be mixtures of copolymers of identical type. Itis advantageous to use uniform fluoropolymers.

In one aspect, the invention relates to a layered product which includesa layer of the fluoropolymer and a rubber. A layered product of thistype can, for example, be built up as follows:

a) an upper layer essentially consisting of the fluoropolymer, and

b) the layer as described, essentially consisting of a mixture of arubber and the fluoropolymer.

The layer a) can adjoin a layer of a fluoropolymer, i.e. a layeredproduct of this type is an intermediate for composite articles. Thisintermediate can, via layer b), adjoin one or more vulcanization-boundrubber layers.

The invention furthermore relates to layered products in which bothouter sides comprise a fluoropolymer, so that a rubber layer is presentonly internally.

Further embodiments of this principle can be devised by a person skilledin the art according to the respective requirements, depending onwhether, for example, the fluoropolymer acting as adhesion promotermeets the requirements for the outer side or whether anotherfluoropolymer is to be employed as outer side.

The amount of fluoropolymer in the layer b) can vary within wide limitsand is usually in the range from 10 to 70% by weight, preferably from 20to 50% by weight.

Suitable rubbers are, as mentioned, natural and synthetic rubber types,i.e. besides natural rubber, the conventional synthetic rubbers based onbutadiene, butadieneacrylonitrile, butadiene-styrene, chloroprene,isoprene, isobutene, ethylene-propylene, ethylene-vinyl acetate,acrylate and epichlorohydrin, and butyl, chlorobutyl, bromobutyl,polysulfide, urethane, fluoro or silicone rubbers, chlorinated andchlorosulfonated polyethylene and hydrogenated acrylonitrile-butadienerubber.

The novel layered products can be produced by mixing a rubber with thefluoropolymer or incorporating one component into the other, for exampleby kneading, then producing a sheet-like or three-dimensional structurefrom this mixture, vulcanizing this, if desired with a layer of rubber,and then applying the fluoropolymer to at least one layer and fixing it.

The fluoropolymer can be applied by conventional methods as a powder, inthe form of a film, melt or as a liquid formulation, for example as asolution or dispersion.

The following materials were employed:

a) A terpolymer consisting of 42% of tetrafluoroethylene units, 20% ofhexafluoropropene units and 38% of vinylidene fluoride units and

b) a butyl rubber mixture consisting of 100 parts of rubber, 100 partsof carbon black and 100 parts of filler (primarily kaolin). The rubberis petroleum-soluble and is vulcanized at 143° C.

EXAMPLE 1

A mixture of 80% of rubber mixture and 20% of terpolymer is prepared andvulcanized in several layers. The layers show very good adhesion.

EXAMPLE 2

A mixture as in Example 1 is converted into a layer and vulcanized witha layer consisting only of the rubber mixture. Once again, the layershows very good adhesion after vulcanization, i.e. the layer containingthe terpolymer imparts very good adhesion to the layer of the rubbermixture.

Using the layer comprising the terpolymer, the layered product thusobtained can be treated in a separate step with a layer offluoropolymer.

EXAMPLE 6

A composite is produced as in Example 5, a solution of the terpolymer inmethyl ethyl ketone is applied to the layer containing the terpolymerand the solvent is evaporated. A film of a second terpolymer of thefollowing composition is applied onto the surface-coating layer thusobtained and vulcanized:

57% of tetrafluoroethylene units,

30% of hexafluoropropene units and

13% of ethylene units.

A composite having good adhesion is obtained.

What is claimed is:
 1. A composition essentially consisting of a rubberand an adhesion promoter comprising a thermoplastic fluoropolymer havingunits of tetrafluoroethylene, hexafluoropropene and vinylidene fluorideand a melting point <250° C.
 2. A composition as claimed in claim 1,wherein the content of adhesion promoter is from 10 to 70% by weight,preferably from 20 to 50% by weight.
 3. A layered product including alayer of a composition as claimed in claim
 1. 4. A layered product asclaimed in claim 3, in which the layer is bonded to a layer of rubber.5. A layered product as claimed in claim 3, in which the layer is bondedto a layer of adhesion promoter.
 6. A layered product essentiallyconsisting of a rubber layer, bonded on both sides to a layer as claimedin claim 3, where, if desired, one or both of the outer layers is/arebonded to a layer of adhesion promoter and, if desired, one or both ofthese layers of adhesion promoter is/are bonded to a further layer ofanother fluoropolymer.
 7. A layered product as claimed in claim 3, inwhich the layer is bonded on the one hand to a rubber layer and on theother hand to a layer of adhesion promoter, which, if desired, is bondedto a layer of another fluoropolymer.
 8. A composition according to claim1 wherein the rubber comprises a fluoroelastomer.
 9. A compositionaccording to claim 1 wherein the rubber comprises a silicone rubber. 10.A composition according to claim 1 wherein the rubber is selected from agroup consisting of natural rubber; synthetic rubbers based uponbutadiene, butadiene-acrylonitrile, butadiene-styrene, chloroprene,isoprene, isobutene, ethylene-propylene, ethylene-vinyl acetate,acrylate and epichlorohydrin; butyl, chlorobutyl, bromobutyl,polysulfide, urethane rubbers; chlorinated and chlorosulfonatedpolyethylene; and hydrogenated acrylonitrile-butadiene rubber.